The present invention relates to an apparatus and method for cleaning a printing mask used in printing and coating various kinds of printing material, for example, solder paste, conductor paste, or insulator paste, on a surface to be printed.
Hitherto, in the fabrication of electronic circuit boards, it has been general practice to use solder paste for soldering electronic components, such as chip components, to a printed board. A solder paste printer has been used for printing and coating solder paste in a desired pattern.
Conventionally, solder paste printing has been carried out using such a method and apparatus as described below. In FIGS. 15 and 16, numeral 1 designates a printed board, 2 a land on which solder paste 4 is to be printed, 3 a solder resist, 5 a metallic mask formed with openings 6 of such a pattern as to enable the solder paste 4 to be printed on the land 2 as desired, and 7 a printing squeegee which is linearly movable on the surface 5a of the mask 5. Printing the solder paste 4 on the printed board 1 is carried out by positioning the mask 5 on the printed board 1 in superposed relation therewith, moving the squeegee 7 linearly as it is held in contact with the mask 5 under a proper printing pressure, thereby allowing the solder paste 4 coated on the mask 5 to be filled in the openings 6 of the mask 5, and then printing and coating the solder paste 4 on the printed board 1 through the mask 5, with the mask 5 spaced from the printed board 1.
When such solder paste printing is carried out successively, as FIG. 16 shows, solder paste 4 is adhered/deposited onto the back 5b of the mask 5. Usually, therefore, the printer is equipped with a cleaner 9 as shown in FIG. 17 so that the solder paste 4 adhered onto the back 5b of the mask 5 can be removed. In that figure, numeral 10 designates a cleaning squeegee, 11 a cleaning paper, 12 a cleaning paper feeder, and 13 a cleaning paper take-up. Shown by 8 is a mask frame.
Operation of such a cleaner 9 for removal of solder paste 4 is carried out in the following way. First, the cleaner 9 is moved in its entirety to a position I and the cleaning squeegee 10 is elevated until it goes into contact with the back 5b of the mask 5 through the cleaning paper 11. While being kept in that condition, the cleaner 9 is moved toward a position II. When the cleaner 9 has been moved to the position II, the cleaning squeegee 10 is lowered, then the cleaning paper take-up 13 is caused to take up the cleaning paper 11 which has performed cleaning, and accordingly fresh cleaning paper 11 is supplied from the cleaning paper feeder 12. Subsequently, the cleaning squeegee 10 is elevated again and the cleaner 9 is moved from the position II and toward the position I in the same way as above described. When the cleaner 9 has moved to the position I, the cleaning squeegee is lowered and the cleaner 9 is brought back to its initial position, whereupon the solder removing operation ends.
Recently, there has been proposed a cleaner 30 which includes, in addition to the above described arrangement of cleaner 9, cleaning means having an air jet portion 15 connected to an air jet mechanism 14, and an air suction portion 17 connected to an air suction mechanism 16, as illustrated in FIG. 18. Shown by 18 is a filter provided in the air suction portion 17.
In a cleaning operation using such a cleaner 30, the air jet portion 15 and the air suction portion 17 are moved to the position I, then the air jet portion 15 is lowered and the air suction portion 17 is elevated so that their respective front ends are brought into contact with the mask 5 at contact portions 20 and 21. The contact portions 20, 21 of the air suction portion 17 contact the back 5b of the mask 5 through the cleaning paper 11 to prevent any air inflow through the contact portions into a suction port 17a and to permit air to be sucked into the suction port 17a only through the openings 6 of the mask 5. With this condition maintained as such, the air jet portion 15 and the air suction portion 17 are synchronously moved toward the position II along the mask 5 to thereby remove solder paste 4 adhered within the openings 6 and on the back 5b of the mask 5. That is, the air suction portion 17 connected to the air suction mechanism 16 is brought into contact with the back 5b of the mask 5 through the cleaning paper 11, and the air jet portion 15 is brought into contact with the surface 5a of the mask 5 in corresponding relation to the air suction portion 17. With air jetting from the air jet portion 15 and with air suction by the air suction portion 17, solder paste 4 adhered within and around the openings 6 of the mask 5 is scattered and/or caused to flow toward the back 5b of the mask 5. Thus, scattered fragments of solder paste 4 are collected onto the cleaning paper 11 and outflow fragments of solder paste 4 adhered onto the back 5b are collected onto the cleaning paper 11 at the contact portion 20 when the cleaner 30 moves from the position I to the position II. After the removal of fragments of solder paste 4 adhered in the openings 6 has been completed in this way, the air jet from the air jet mechanism 14 and air suction by the air suction mechanism 16 are stopped. Then, the air jet portion 15 is elevated, and the air suction portion 17 is lowered. Thereafter, the cleaner is made to return to its initial condition, its cleaning operation being thus ended.
Such a cleaning method including the steps of air jetting and air suction has an advantage over the cleaning method illustrated in FIG. 17 in that solder paste 4 adhered within the openings 6 of the mask 5 and onto the inner periphery thereof can be removed, it being thus possible to improve removal efficiency with respect to solder paste 4.
In the above described cleaner 30, however, the contact portions 20, 21 of air suction portion 17 which contact the back 5b of the mask 5 are merely intended to define a suction port 17a to permit air suction into the suction port 17a only through the openings 6 as stated above. As such, in the prior art there has been no technical concept that the back 5b of the mask 5 be positively cleaned by means of the contact portions 20, 21. As FIG. 19A shows, therefore, the span III of the contact portions 20, 21 each as viewed in the direction of movement of the cleaner 30 is designed to be not more than 1 mm. In the cleaner 30, the span IV of the suction port 17a as viewed in the direction of movement of the cleaner 30 is 3 mm. In FIGS. 19A, 19B, and 19C, the air jet portion 15 is not shown.
In the cleaner 30 of the prior art construction, therefore, the areas of the contact portions 20, 21 which go into contact with the mask 5 are small. Thus, as FIGS. 19A to 19C show, along with the movement of the air suction portion 17 from the position I toward the position II, the surface of those portions 11a, 11b of the cleaning paper 11 which are held between the back 5b of the mask 5 and the contact portions 20, 21, and adjacent portions thereof will be readily covered with a mass of solder paste 4. With the cleaning paper 11 so covered with solder paste 4, it is impossible to collect the mass of solder paste 4 adhered on the back 5b of the mask 5, with the result that some solder paste 4 remains in the openings 6 and on the back 5b of the mask 5 even after the end of the cleaning operation. This poses a disadvantage that in a subsequent printing process there might occur such printing defects as earlier mentioned, including poor off-plate effects and solder ball bridges. In FIGS. 19A-19C, solder paste 4 is more precisely illustrated, with spherical solder particles contained therein being shown on an enlarged scale.